Method and apparatus for semiactive reduction of pressure oscillations in a hydraulic system

ABSTRACT

A method and an apparatus for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or strip handling installation for iron, steel or aluminum materials has the following method steps in the stated sequence: 
     a) detection of a pressure signal by a pressure sensor by permanent measurement of a pressure in the hydraulic system;
 
b) determination of an alternating component of the pressure signal;
 
c) determination of at least one manipulated variable, which varies over time, in real time with the aid of a regulator, taking account of the alternating component;
 
d) application of the manipulated variable to at least one actuator, with the actuator changing a natural frequency of an oscillation damper which is connected to the hydraulic system, and thus reducing an amplitude of the pressure oscillations in the hydraulic system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2009/066020 filed Nov. 30, 2009, which designates the United States of America, and claims priority to Austrian Application No. A1896/2008 filed Dec. 5, 2008, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or strip handling installation for iron, steel or aluminum materials.

BACKGROUND

It is known that periodically occurring pressure oscillations in hydraulic systems cause various problems, for example excessive noise development, reduction in the life of components, interference with control loops, etc. Pressure oscillations may be caused either in the hydraulic system itself, for example as a result of non-uniformity of the feed rate of pumps or by the operation of valves etc., or else may be caused externally, for example by periodic load fluctuations on hydraulic cylinders or motors. It is also known that severe pressure oscillations can occur in the hydraulic system, particularly in the case of highly dynamic hydraulic systems, for example consisting of a highly dynamic continuous-operating hydraulic valve (for example an electrically operated proportional valve or servo valve) and a hydraulic cylinder or motor.

It has been found that severe pressure oscillations can also occur in the hydraulic systems of modern rolling mills or strip handling installations—for example if the rollers are positioned hydraulically—, which can lead to a reduction in the life of components, or else to considerable damage to the rolling mill stands and/or to defects in the rolling material. This is due in particular to the fact that, on the one hand—because of higher rolling forces or speeds—hydraulic systems are used which react ever more quickly (more dynamically), and on the other hand—because of more stringent requirements for the reaction time and economy—the damping in the hydraulic systems is reduced (for example the viscous damping in the seals of cylinders).

DE 4 302 977 A1 discloses an apparatus for active suppression of pressure oscillations in a hydraulic unit, which apparatus has a pressure sensor, a regulating device with an associated amplifier, and a volume compensator. The document does not disclose specific rules for the method to be carried out or any more detailed indications of an advantageous use of the apparatus in a hydraulic system for a rolling mill or strip handling installation.

Because of the high frequencies of the pressure oscillations to be suppressed and the high pressures in modern hydraulic systems, the actuators for active oscillation compensation systems, in particular, are subject to very stringent requirements. As a result of this, the actuators are no longer compact (in particular they have a large volume) and, because of the stringent requirements for the power density, it is only possible to use very high-quality and expensive actuators. A further disadvantage of active oscillation compensation systems is that energy is additionally introduced into the hydraulic system via the actuator, fundamentally making the stability of the overall system worse and, particularly in the case of a regulator which is not set exactly, this can even lead to a deterioration in the system response (that is to say, in some circumstances, the amplitude of the pressure oscillations is not reduced, but is even amplified).

SUMMARY

According to various embodiments, a method and an apparatus for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or a strip handling installation can be provided, by means of which pressure oscillations which occur can be effectively reduced by means of a simple and low-cost apparatus.

According to an embodiment, a method for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or strip handling installation for iron, steel or aluminum materials, may comprise the following method steps in the stated sequence: a) detection of a pressure signal by means of a pressure sensor by permanent measurement of a pressure in the hydraulic system; b) determination of an alternating component of the pressure signal; c) determination of at least one manipulated variable, which varies over time, in real time with the aid of a regulator, taking account of the alternating component; d) application of the manipulated variable to at least one actuator, with the actuator changing a natural frequency of an oscillation damper which is connected to the hydraulic system, and thus reducing an amplitude of the pressure oscillations in the hydraulic system.

According to a further embodiment, the alternating component can be subjected to bandpass filtering. According to a further embodiment, the actuator may change a volume in the oscillation damper, which volume corresponds to the manipulated variable. According to a further embodiment, the actuator may change the volume of a Helmholtz resonator or over the active length of a λ/4 resonator. According to a further embodiment, the method can be applied to a hydraulic system of a positioning cylinder of a rolling mill stand.

According to another embodiment, an apparatus for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or strip handling installation for iron, steel or aluminum materials, may have a pressure sensor, which is connected to the hydraulic system, for detection of a pressure signal, an element for determination of an alternating component of the pressure signal, to which the pressure signal can be supplied, at least one regulating apparatus, to which the alternating component can be supplied and with the aid of which at least one manipulated variable can be determined, at least one oscillation damper which is connected to the hydraulic system, and at least one actuator, which is connected to the oscillation damper and has a variable volume, to which the manipulated variable can be supplied and via which a resonator volume of the oscillation damper can be varied.

According to a further embodiment of the apparatus, the oscillation damper can be in the form of a λ/4 or Helmholtz resonator. According to a further embodiment of the apparatus, the actuator can be in the form of an electrical lifting spindle actuator or hydraulic actuator. According to a further embodiment of the apparatus, the apparatus can be connected to a hydraulic valve and a hydraulic cylinder of a hydraulic roller positioning means.

According to yet another embodiment, the method as described above or the apparatus as described above can be used for the processing and/or production of metallic materials, in particular in a composite casting and rolling installation.

According to a further embodiment of the use, the composite casting and rolling installation can be a thin-strip casting installation or a thin-slab casting installation (ESP).

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and features will become evident from the following description of exemplary embodiments, which are not restrictive, with reference being made to the following figures in which, as follows:

FIG. 1 shows a layout of a controlled system for semiactive reduction of pressure oscillations in a hydraulic system,

FIG. 2 shows a layout of an apparatus according to various embodiments for reduction of pressure oscillations in a hydraulic system in a rolling mill, and

FIGS. 3 and 4 show layouts of an oscillation damper with an integrated actuator.

DETAILED DESCRIPTION

According to various embodiments, a method of the type mentioned initially, may comprise the following method steps in the stated sequence:

a) detection of a pressure signal by means of a pressure sensor by permanent measurement of a pressure in the hydraulic system; b) determination of an alternating component of the pressure signal; c) determination of at least one manipulated variable, which varies over time, in real time with the aid of a regulator, taking account of the alternating component; d) application of the manipulated variable to at least one actuator, with the actuator changing a natural frequency of an oscillation damper which is connected to the hydraulic system, and thus reducing an amplitude of the pressure oscillations in the hydraulic system.

In this case, a pressure signal is detected by means of a pressure sensor (for example by means of a piezoelectric, piezoresistive or strain gauge measurement cell), by permanently measuring a pressure in a hydraulic system, for example a rolling mill stand in a rolling installation. A hydraulic system means a section (typically a hydraulic circuit or a hydraulic axis) of a hydraulic installation, which are hydraulically connected to one another, for example the area between a hydraulic valve and a hydraulic cylinder, including the hydraulic lines or hoses. An alternating component is then determined from the pressure signal, that is to say a constant component of the pressure signal is removed, and is supplied to a regulator. The alternating component can be determined either by an electronic filter module or by a digital filter (for example removal of the constant component by means of a sliding window consisting of n measured values of the pressure oscillations (filter order n); however, it is of course also possible for the DC component to be removed only in the regulator algorithm); alternatively, the alternating component can also be determined by means of a piezoelectric pressure sensor and a charge amplifier, which is either connected downstream from the pressure sensor or is integrated in the pressure sensor. The regulator determines at least one manipulated variable, which varies over time, in real time taking account of the alternating component of the pressure signal, and this manipulated variable is applied to at least one actuator, thus varying a natural frequency of an oscillation damper which is connected to the hydraulic system. In this application, an oscillation damper means an element, which is passive per se, for oscillation damping, for example a λ/4 resonator (“side branch resonator”), a Helmholtz resonator etc. “Semiactive reduction of pressure oscillations” is intended to mean reduction of an amplitude of pressure oscillations in a hydraulic system by means of a passive oscillation damper, in which case the natural frequency of the passive oscillation damper can be varied by means of an actuator. A particularly major reduction in the amplitude of the pressure oscillations can be achieved by deliberately applying the manipulated variable to the actuator in order to vary a natural frequency of the oscillation damper, such that the natural frequency of the oscillation damper is made to match a frequency of the pressure oscillation. The manipulated variable signal can be transmitted from the regulator to the actuator with or without the use of cables (for example by radio).

In one embodiment of the method, the alternating component of the pressure signal is subjected to bandpass filtering. This filtering makes it possible to filter out of the alternating component either particularly disturbing frequency components (which for example coincide with a natural frequency of the rolling mill stand or of a subsystem) or frequency components with a high amplitude or intensity (for example from a spectrum of an FFT (Fast Fourier Transform) or PSD (Power Signal Density)), and to supply these to the regulator.

In one embodiment, the actuator changes a volume in the oscillation damper, which volume corresponds to the manipulated variable, with the volume corresponding to the manipulated variable (a manipulated variable of zero corresponds, for example, to the actuator being in a non-deflected (neutral) position; a maximum manipulated variable may then, for example, correspond to a maximum deflection in one direction), thus varying a natural frequency of the oscillation damper.

The method according to various embodiments can be carried out in a particularly advantageous manner if the actuator changes the volume of a Helmholtz resonator or the active length of a λ/4 resonator. The natural frequency of these oscillation dampers can be adjusted in a simple manner.

Since the pressure oscillations in a hydraulic system of a positioning cylinder of a stand for rolling iron, steel or aluminum materials have a direct influence on the quality of the rolling material, and are therefore particularly disturbing, it is advantageous to use the method according to various embodiments for a hydraulic system for a positioning cylinder for a rolling mill stand.

In order to allow the method according to various embodiments to be implemented as directly as possible it is advantageous for the apparatus to have a pressure sensor, which is connected to the hydraulic system, for detection of a pressure signal, an element for determination of an alternating component of the pressure signal, to which the pressure signal can be supplied, at least one regulating apparatus, to which the alternating component can be supplied and with the aid of which at least one manipulated variable can be determined, at least one oscillation damper which is connected to the hydraulic system, and at least one actuator, which is connected to the oscillation damper and has a variable volume, to which the manipulated variable can be supplied and via which a resonator volume of the oscillation damper can be varied. A natural frequency of the oscillation damper can in turn be adjusted via the resonator volume, thus making it possible to match the natural frequency to a frequency of the pressure oscillations.

The natural frequency can be adjusted particularly easily if the oscillation damper is in the form of a λ/4 or Helmholtz resonator.

A particularly low-cost apparatus can be achieved if the actuator is in the form of an electrical lifting spindle actuator or hydraulic actuator. Since the actuator can be adjusted slowly—in comparison to systems with active oscillation compensation—commercially available electrical or hydraulic actuators are completely adequate.

The apparatus according to various embodiments can be used in a particularly advantageous manner if the apparatus is connected to a hydraulic valve and a hydraulic cylinder of a hydraulic roller positioning means. This installation makes it possible to reduce oscillations on the rollers of a rolling mill stand particularly easily, thus making it possible to effectively improve the quality of the rolling material. The installation is particularly compact when the apparatus is installed in an intermediate plate of the hydraulic valve.

Particular advantages result from the use in a composite casting and rolling installation, particularly in thin-strip casting installations, and very particularly preferably in two-roller casting installations and thin-slab casting installations of the ESP (Endless Strip Production) type.

FIG. 1 shows the basic design of a controlled system for reduction of pressure oscillations in a hydraulic system of a rolling mill. A pressure signal for a pressure in the hydraulic system is detected via a pressure sensor 1, the pressure signal 2 is supplied to a high-pass filter 3 (for details relating to the electronic circuit, see for example page 35 in P. Horowitz, W. Hill. The Art of Electronics, Cambridge University Press, Second Edition, 1989), which determines the alternating component 2′ of the pressure signal 2, and supplies this to a regulator 4. This regulator 4 uses a control law to calculate a manipulated variable 6, which varies over time, in real time, taking account of the alternating component 2′. The manipulated variable signal is then supplied to an amplifier 8, which operates an actuator 9, in the form of an electrical lifting spindle actuator. The actuator 9 varies the resonator volume of an oscillation damper 13 which is in the form of a Helmholtz resonator, with the change in the resonator volume corresponding to the manipulated variable 6. The change in the resonator volume varies a natural frequency of the oscillation damper 13, thus matching the natural frequency of the oscillation damper to a frequency of the pressure oscillation. This measure reduces the amplitude of the pressure oscillation in the hydraulic system in a very simple but effective manner.

FIG. 2 schematically illustrates an apparatus for suppression of pressure oscillations in a hydraulic system of a rolling mill stand for iron, steel or aluminum materials. A pressure signal 2 is detected by means of a pressure sensor 1, by permanent measurement of a pressure in a hydraulic system 10, with the hydraulic system comprising a hydraulic valve 11, a hydraulic cylinder 12 and a hydraulic line. The hydraulic system is used to position a roller 14 for rolling a rolling material 15. In this case, the pressure sensor 1 may be located either in the section between an oscillation damper 13 and the hydraulic cylinder 12 (as shown), or in the section between the hydraulic valve 11 and the oscillation damper 13. It is, of course, also possible to arrange a plurality of pressure sensors between the oscillation damper 13 and the hydraulic cylinder 12, or between the hydraulic valve 11 and the oscillation damper 13. The pressure signal 2 is transmitted to a digital regulator 4, which determines a frequency band of the alternating component of the pressure signal, and calculates a manipulated variable 6, which varies over time, with the assistance of a control algorithm. The manipulated variable is supplied, after amplification in an amplifier which is not illustrated, to an actuator 9 which is in the form of an electrical lifting spindle actuator and which varies a resonator volume, corresponding to the manipulated variable 6, in the oscillation damper 13, which is in the form of a Helmholtz resonator, as a result of which a natural frequency of the oscillation damper 13 is matched to a frequency of the pressure oscillations, thus reducing the amplitude of a pressure oscillation.

FIG. 3 shows an oscillation damper 13, which is in the form of a Helmholtz resonator and has an integrated actuator 9. A manipulated variable 6 can be supplied to the actuator 9, by which means it is possible to vary the resonator volume V, V=LS, where L is the length and S is the cross-sectional area of the resonator volume of the Helmholtz resonator. A natural frequency of the oscillation damper 13 can be varied by varying the resonator volume V, with the natural frequency f of the Helmholtz resonator being defined by the condition:

$f = {\frac{c}{2\pi}\sqrt{\frac{S^{\prime}}{L^{\prime}\underset{\underset{V}{}}{LS}}}}$

In this case, c is the speed of sound in the hydraulic liquid, S′ is the cross-sectional area and L′ is the length in the resonator neck, L is the length and S is the cross-sectional area of the resonator volume V (cf. Chapter 8.3.3 Resonators in the textbook, H. Kuttruff, Acoustics—An Introduction, Taylor and Francis, 2007).

FIG. 4 shows an oscillation damper 13, which is in the form of a λ/4 resonator and has an integrated actuator 9. A manipulated variable 6 can be supplied to the actuator 9, thus allowing the active length L of the λ/4 resonator to be varied. A natural frequency of the oscillation damper 13 can be varied by varying the active length L, with the natural frequency f of the λ/4 resonator being given by the condition:

$f = {\frac{1}{4}\frac{c}{L}}$

In this case, c is the speed of sound in the hydraulic liquid, and L is the active length.

The method according to various embodiments or the apparatus may, of course, be used in any desired hydraulic systems for mobile hydraulics or industrial hydraulics.

LIST OF REFERENCE SYMBOLS

-   1 Pressure sensor -   2 Pressure signal -   2′ Alternating component of the pressure signal -   3 Bandpass filter -   4 Regulator -   6 Manipulated variable -   8 Amplifier -   9 Actuator -   10 Hydraulic system -   11 Hydraulic valve -   12 Hydraulic cylinder -   13 Oscillation damper -   14 Roller -   15 Rolling material 

1. A method for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or strip handling installation for iron, steel or aluminum materials, comprising the following method steps in the stated sequence: a) detecting a pressure signal by means of a pressure sensor by permanent measurement of a pressure in the hydraulic system; b) determining an alternating component of the pressure signal; c) determining at least one manipulated variable, which varies over time, in real time with the aid of a regulator, taking account of the alternating component; d) applying the manipulated variable to at least one actuator, with the actuator changing a natural frequency of an oscillation damper which is connected to the hydraulic system, and thus reducing an amplitude of the pressure oscillations in the hydraulic system.
 2. The method according to claim 1, wherein the alternating component is subjected to bandpass filtering.
 3. The method according to claim 1, wherein the actuator changes a volume in the oscillation damper, which volume corresponds to the manipulated variable.
 4. The method according to claim 3, wherein the actuator changes the volume of a Helmholtz resonator or over the active length of a λ/4 resonator.
 5. The method according to claim 1, wherein the method is applied to a hydraulic system of a positioning cylinder of a rolling mill stand.
 6. An apparatus for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or strip handling installation for iron, steel or aluminum materials, having a pressure sensor, which is connected to the hydraulic system, for detection of a pressure signal, an element for determination of an alternating component of the pressure signal, to which the pressure signal can be supplied, at least one regulating apparatus, to which the alternating component can be supplied and with the aid of which at least one manipulated variable can be determined, at least one oscillation damper which is connected to the hydraulic system, and at least one actuator, which is connected to the oscillation damper and has a variable volume, to which the manipulated variable can be supplied and via which a resonator volume of the oscillation damper can be varied.
 7. The apparatus according to claim 6, wherein the oscillation damper is in the form of a λ/4 or Helmholtz resonator.
 8. The apparatus according to claim 6, wherein the actuator is in the form of an electrical lifting spindle actuator or hydraulic actuator.
 9. The apparatus according to claim 6, wherein the apparatus is connected to a hydraulic valve and a hydraulic cylinder of a hydraulic roller positioning means.
 10. The method according to claim 1, wherein the method is used for at least one of processing and production of metallic materials or in a composite casting and rolling installation.
 11. The method according to claim 10, wherein the composite casting and rolling installation being a thin-strip casting installation or a thin-slab casting installation (ESP).
 12. The method according to claim 10, wherein the alternating component is subjected to bandpass filtering.
 13. The method according to claim 10, wherein the actuator changes a volume in the oscillation damper, which volume corresponds to the manipulated variable.
 14. The method according to claim 13, wherein the actuator changes the volume of a Helmholtz resonator or over the active length of a λ/4 resonator.
 15. The method according to claim 10, wherein the method is applied to a hydraulic system of a positioning cylinder of a rolling mill stand.
 16. A method for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or strip handling installation for iron, steel or aluminum materials, comprising the steps of: providing an apparatus for semiactive reduction of pressure oscillations in a hydraulic system of a cold or hot rolling mill or strip handling installation for iron, steel or aluminum materials, having a pressure sensor, which is connected to the hydraulic system, for detection of a pressure signal, an element for determination of an alternating component of the pressure signal, to which the pressure signal can be supplied, at least one regulating apparatus, to which the alternating component can be supplied and with the aid of which at least one manipulated variable can be determined, at least one oscillation damper which is connected to the hydraulic system, and at least one actuator, which is connected to the oscillation damper and has a variable volume, to which the manipulated variable can be supplied and via which a resonator volume of the oscillation damper can be varied; and using used the apparatus for at least one of processing and production of metallic materials or in a composite casting and rolling installation.
 17. The method according to claim 16, wherein the oscillation damper is in the form of a λ/4 or Helmholtz resonator.
 18. The method according to claim 16, wherein the actuator is in the form of an electrical lifting spindle actuator or hydraulic actuator.
 19. The method according to claim 16, wherein the apparatus is connected to a hydraulic valve and a hydraulic cylinder of a hydraulic roller positioning means.
 20. The method according to claim 16, wherein the composite casting and rolling installation being a thin-strip casting installation or a thin-slab casting installation (ESP). 